Housing for a wheel speed sensor having coil bobbin suspended within the housing

ABSTRACT

A sensor for detecting the angular velocity of a rotating member. The sensor includes a bobbin having an exterior defining an annular recess and a coil within the recess. The bobbin also has a generally cylindrical aperture and supports a probe and a permanent magnet in the aperture. The housing is secured to the bobbin and the housing and bobbin include tapered inner and outer surfaces, respectively, that are made to form a wedge fit seal between the bobbin and the housing to prevent the introduction of molding material during the overmolding process. The bobbin also includes supports for supporting the lead wires extending between the coil and the terminals.

This is a divisional of application Ser. No. 08/363,900, filed Dec. 27,1994, now U.S. Pat. No. 5,629,618 entitled "IMPROVED HOUSING FOR A WHEELSPEED SENSOR" and issued May 13, 1997.

BACKGROUND OF THE INVENTION

The invention relates to a sensor for detecting the angular velocity ofa rotating element and particularly to an improved housing for avariable reluctance speed sensor.

It is known in the art to mount a speed sensor in the transmission or inthe bearing or wheel end assembly of a vehicle such as a truck or anautomobile. Typically, the sensor includes a coil mounted on a bobbinwhich is inserted into a housing. The sensor measures the angularvelocity of rotating elements within the transmission or bearingassembly. However, the environments in which the sensors are employedcan be extremely harsh and the sensors must be capable of withstanding asignificant amount of repeated temperature variations over a wide rangeof temperatures (thermal cycling), intense vibration and exposure tocorrosive elements. In order to seal the sensor from the environment thebobbin is connected to the housing and the combination is overmolded toprovide a molded seal between the bobbin and the housing.

SUMMARY OF THE INVENTION

One problem with known sensors is that if the bobbin and the housing donot form a mechanical seal between one another, the molding material mayflow into the housing and damage the coil.

Another problem with known sensors is that if the lead wires of the coilare not adequately secured to the bobbin, the intense vibration of thevehicle may cause mechanical fatigue of the leads resulting indegradation or complete failure of the sensor. Alternatively, if thecoil and lead wires are too securely fixed to some structure on thesensor, or if the portion of the bobbin holding the coil engages thehousing, the constant thermal cycling may place mechanical stresses onthe coil and lead wires and eventually cause either the coil or the leadwires to break.

Another problem has been that of positioning the probe close enough tothe rotating element so that the signal generated by the sensor isstrong. The closer the probe is to the rotating element, the better orstronger the signal generated by the coil.

Therefore, it is desirable to provide a speed sensor having a housingthat provides a sealed environment for the bobbin and coil and iscapable of withstanding exposure to thermal cycling, vibration andcorrosive elements without damage to the sensor and that generates asignal sufficient to measure the speed of the rotating element.

Accordingly, the invention provides a sensor including means forsupporting the skeined (i.e., braided for increased strength) lead wiressecurely against the exterior of the bobbin to prevent excess vibrationof and stress on the lead wires, a tapered or wedge fit lock between thebobbin and the housing to prevent molding material from flowing into thehousing during the overmolding process, a top hat or shoulder on thebobbin to act as a material shield which redirects material flow duringthe over-mold process, and to position and support the coil in thehousing and prevent contact between the coil and the housing, and animproved housing/probe interface to position the probe near the rotatingelement without weakening the housing.

More specifically, the bobbin has an interior surface defining agenerally cylindrical aperture and an exterior surface. The exteriorsurface defines an annular recess, an upper portion having a taperedouter surface and an annular shoulder.

A coil is mounted on the bobbin and within the recess. The coil includesa pair of skeined lead wires that are soldered to the ends of respectiveterminals, supported by the bobbin. Each lead wire includes a portionextending between the recess and the respective terminal. The bobbinincludes supporting means mounted on the exterior surface of the bobbin.The supporting means includes a pair of supporting shelves each havingan end and a tapered tang or extension projecting from the end. The tangis spaced from the exterior surface of the bobbin and a ramped chute isbetween the exterior surface and the bobbin. The lead wires extend fromthe coil and through the ramped chute to the respective shelves. Eachshelf supports the portion of the lead wire extending between the recessand the terminal. The tang and the shelf secure and position thatportion of the respective lead wire against the bobbin to preventseparation of that portion during thermal cycling or vibration of thesensor.

The sensor also includes a generally cylindrical housing constructed andarranged to receive at least a portion of the bobbin so as to enclosethe coil within the housing. The housing includes an end wall having aninner surface. In one embodiment, the inner surface includes a recessformed therein and an engaging surface surrounding the recess. Thehousing also includes a generally cylindrical sidewall connected to theend wall. The generally cylindrical sidewall has a tapered inner surfaceand an annular rim opposite the end wall. The tapered inner surface ofthe housing engages the tapered outer surface of the bobbin to provide awedge fit seal or lock between the bobbin and the housing. The sealprevents the introduction of molding material into the housing duringthe overmolding process. The bobbin is completely inserted within thehousing when the annular rim on the housing engages the annular shoulderon the bobbin. The annular shoulder provides a positive stop againstover insertion of the bobbin into the housing, and positions andsupports the bobbin within the housing so that no portion of the bobbinother than the outer tapered surface of the bobbin, engages the innersurface of the housing. The precise positioning of the bobbin within thehousing prevents contact between the housing and the portion of thebobbin defining the annular recess. Such contact could result in stressduring thermal cycling or vibration of the sensor and this stress couldin turn result in damage to the coil mounted on the bobbin.

A pole piece or probe of ferromagnetic material is mounted within thecylindrical aperture in the bobbin. The probe has a generally circularend surface and the end surface includes a centrally positioned raisedportion and periphery surrounding the raised portion. In one embodiment,the periphery engages the engaging surface of the end wall of thehousing so that the raised portion of the probe end surface extends intothe recess in the end wall of the housing.

A principal feature of the invention is the provision of a sensor havinga bobbin and housing for providing a seal with the bobbin to prevent theintroduction of contaminants and molding materials into the housingduring the overmolding process.

Another feature of the invention is the provision of a sensor having abobbin and a housing therefor, the bobbin and housing interacting tocompletely suspend the coil and that portion of the bobbin supportingthe coil within the housing, thereby preventing transmission of stressto the coil during thermal cycling of the apparatus.

Another feature of the invention is the provision of a sensor having abobbin for supporting the skeined leads of a coil.

Another feature of the invention is the provision of a sensor having aprobe that engages the end wall of the housing to position the probesufficiently close to the rotating element to measure the angularvelocity of the rotating element.

Other features and advantages of the invention will become apparent tothose skilled in the art upon review of the following detaileddescription, claims, and drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an overmolded speed sensor.

FIG. 2 is a perspective view of the sensor before the sensor has beenovermolded and showing the housing with the bobbin inserted in thehousing.

FIG. 3 is an exploded perspective view of the sensor showing the bobbinand the housing.

FIG. 4 is a front elevational view of the bobbin of the sensor.

FIG. 5 is a view taken along line 5--5 in FIG. 4, but differs from FIG.4 in that FIG. 5 shows the housing mounted on the bobbin.

FIG. 6 is a rear elevational view of the bobbin.

FIG. 7 is an enlarged partial view of the bobbin showing the supportsfor the skeined leads of the coil.

FIG. 8 is a partial cross section taken along line 8--8 in FIG. 6.

FIG. 9 is a partial, sectional view of a speed sensor that is anotherembodiment of the invention.

Before one embodiment of the invention is explained in detail, it is tobe understood that the invention is not limited in its application tothe details of construction and the arrangements of components set forthin the following description or illustrated in the drawings. Theinvention iscapable of other embodiments and is capable of beingpracticed or of being carried out in various ways. Also, it is to beunderstood that the phraseology and terminology used herein is for thepurpose of description and should not be regarded as limiting.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Shown in FIG. 1 of the drawings is a sensor 10 for detecting the angularvelocity of a rotating member (not shown) such as the rotating bearingelement of a bearing assembly in a vehicle wheel or a rotating elementin the transmission of a vehicle such as an automobile or truck. As bestshown in FIGS. 2 and 3 of the drawings, the sensor 10 includes a bobbinorbobbin assembly 14 that fits within a housing 18. While the housingshown in the drawings is generally cylindrical (i.e., circular incross-section), it should be understood that housings having differentcross-sectional configurations (e.g., oval, rectangular, pentagonal,hexagonal, etc.) are appropriate. The combination of the housing 18 andbobbin 14 is overmolded to form the finished product (shown in FIG. 1)andcompletely seal the bobbin 14 within the housing 18. The process ofovermolding creates a connector or fitting 22 (FIG. 1 ) allowing thesensor 10 to be connected to an input connector (not shown) forconductingthe electrical signals generated by the sensor 10 to signalconditioning circuitry (also not shown).

The bobbin 14 is a generally cylindrical injection molded plastic shell.Referring specifically to FIGS. 4, 5, and 6, the bobbin 14 has oppositeends 26 and 30 and a longitudinal axis 34 (FIG. 4) extending between theends 26 and 30. The bobbin 14 has an interior surface 38 (FIG. 5)defininga cylindrical aperture 42 extending between the ends 26 and 30and along the axis 34. As best seen in FIG. 5, the interior surface 38has first andsecond portions 46 and 50 and an annular shoulder orstepped portion 54 between the first and second portions 46 and 50 suchthat the first portion 46 of aperture 42 is narrower in diameter thanthe second portion 50 of aperture 42.

Still referring to FIG. 5, the bobbin 14 also includes an exteriorsurface 60 which defines an end portion or support 58 having an annularrecess 62,an annular shoulder 66 and a tapered outer surface 70 betweenthe end portion 58 and the annular shoulder 66.

Shown in FIGS. 4-5, a pair of electrically conductive leads 74 aremolded into the bobbin 14. Each lead 74 includes opposite ends 78 (FIG.4 only) and 82. One of the ends 78 defines a terminal 86 positionedbetween the recess 62 and the tapered surface 70 of the bobbin exteriorsurface 60. The other of the ends 82 extends beyond the annular shoulder66 and defines a male connecting pin 90. The male connecting pin 90provides an electrical connection between the sensor 10 and the signalconditioning circuitry (not shown).

An induction coil 94 is mounted in the annular recess 62 of the bobbin14. The coil 94 is an electrical conductor such as copper wire that iswound around bobbin 14 and within the annular recess 62. The electricalproperties of the coil 94 may vary depending upon the number of turns ofthe electrical conductor and the thickness or gauge of the conductor.These variables are dictated by the particular application in which thesensor 10 is being used. A piece of electrically insulating tape 98(FIG. 4) is wound around the coil 94 to secure the coil 94 in place inthe recess 62.

As shown in FIG. 6, the coil 94 terminates with a pair of electricallyconductive lead wires 102. The lead wires 102 include portions 106(FIGS. 6 and 8) that extend in opposite directions around the exteriorof the bobbin 14, between the annular recess 62 and the respectiveterminals 86. As best shown in FIGS. 6, 7, and 8, the exterior of thebobbin 14 includesa support 110 for each lead wire portion 106. Thesupports 110 are mirror images of one another (FIG. 8). The supports 110each terminate at an end portion 118 adjacent the rear (FIG. 6) of thebobbin 14. The end portions 118 of the supports 110 each defineoppositely facing tangs 122 spaced from the exterior surface 60 andbetween the recess 62 and the shoulder 66so as to form tapered or rampedchutes 126 (only one of which is shown in FIG. 8) sloping from theannular recess 62 in the bobbin 14 to the respective supports 110. Thelead wires 102, which in the preferred embodiment are skeined (i.e.,braided for increased strength), extend fromannular recess 62, aroundthe respective tangs 122, through chutes 126, to supports 110 andradially around the exterior surface 60 of bobbin 14 to the respectiveterminals 86. The lead wires 102 are held in place in the respectivechutes 126 by tangs 122 and are soldered to the respective terminals 86in order to make a secure electrical connection between the lead wires102 of the coil 94 and the electrically conductive leads 74 molded intothe bobbin 14. Supporting the lead wires 102 between the tangs122 andthe exterior surface 60 of bobbin 14 secures the lead wires 102 againstthe exterior surface 60 of the bobbin 14 and prevents them fromseparating from the exterior surface 60 of the bobbin 14 in response tovibration of the vehicle or stress resulting from thermal cycling of thesensor 10 and reduces the risk of damage due to mechanical fatigue ofthe lead wires 102.

Referring now to FIG. 9, the sensor 10 also includes a probe 130 made offerromagnetic material. The probe 130 is mounted within the cylindricalaperture 42 in the bobbin 14. The probe 130 includes a cylindricalportion134 having a first end portion 138 and a second end portion 142.The first end portion 138 of the cylindrical portion 134 of the probe130 includes an end surface 162. A base portion 146 is connected to thesecond end portion 142. The base portion 146 has a diameter larger thanthe diameter of the first portion 46 of the interior surface 38 definingcylindrical aperture 42 in the bobbin 14 and the base portion 146includes first and second opposite side surfaces 154 and 158,respectively. The first side surface 154 faces the stepped portion 54 ofthe interior surface 38.

A permanent magnet 174 is also mounted within the cylindrical aperture42 of the bobbin 14. The magnet 174 engages the base portion 146 of theprobe130 to provide a permanent source of magnetic flux. The contactbetween theprobe 130 and the magnet 174 provides a low reluctance fluxpath for the magnetic field generated by the magnet 174.

Still referring to FIG. 9, the housing 18 of sensor 10 has a cylindricalsidewall 178 having opposite ends 182 and 186 and an end wall 190connected to the sidewall 178 adjacent end 182. The cylindrical sidewall178 has a generally cylindrical inner surface 194 that is tapered andhavea relatively small taper angle of less than about 10 degrees (FIG.5) to form a frustoconical shape and thereby form a sealing meansbetween the bobbin 14 and the housing 18. As shown in FIG. 5, thesealing means is a wedge fit seal or taper lock between the taperedouter surface 70 of the exterior surface 60 of the bobbin 14 and thetapered inner surface 194, which is generally complementary to theexterior surface 60. In other words, in the illustrated embodiment thesurface portions are held in place by frictional engagement only. Thehousing 18 includes an annular rim 198 adjacent the end 186 of thesidewall 178. The rim 198 abuts against the annular shoulder 66 on thebobbin 14 and provides a positive stop for positioning the bobbin 14within the housing 18.

Referring still to FIG. 9, the end wall 190 of the housing 18 includesan inner surface 202. The inner surface 202 has a recessed surface 206and the probe end surface 162 engages the recessed surface 206 toposition theprobe near the rotating element (not shown). As shown inFIGS. 5 and 9, at the end 182 of the housing, the end wall 190 is closedand does not include an opening through which the probe could extend.Thus, the end portion of the housing comprises a closed end.

The housing 18 is dimensioned and arranged so that the end portion 58 ofthe bobbin 14 supporting the coil 94 is completely suspended within thehousing 18 such that the end portion 58 of the bobbin 14 is spaced fromthe inner surface 202 of the housing 18. Engagement of the end portion58 with the inner surface 202 of the housing 18 could stress the coil 94and cause damage thereto during thermal cycling of the sensor 10.

The housing 18 also includes an outer surface 214 and a plurality ofradially outwardly extending annular ribs 218 on the outer surface 214of the housing 18 and adjacent the rim 198 of the housing 18. The ribs218 atleast partially melt during the overmolding process and combinewith the overmolded material to form a secure seal around the bobbin 14and with the housing 18 to prevent the introduction into the sensor 10of corrosiveelements.

The rotating element (not shown) typically includes a plurality of teethmounted thereon so that as the rotating element moves past the end wall190 of the housing 18, the air gap between the rotating element and thesensor 10 varies. This variation results in a variation in theelectrical signal generated on the coil 94 of the sensor 10.

FIG. 5 illustrates another embodiment of the invention. Like parts areidentified using like reference numerals. The probe end surface 162 hasa periphery 166 and a centrally positioned raised portion 170 surroundedby the periphery 166. The raised portion 170 is centered on the axis 34(which is shown only in FIG. 4). Additionally, the inner surface 202 hasan engaging surface 210 surrounding the recessed surface 206. Theperiphery 166 of the probe end surface 162 engages the engaging surface210 of the housing 18 so that the raised portion 170 of the probe 130extends into the recess formed by the recessed surface 206 in the endwall190 of the housing 18. The probe 130 is supported by the strongerportion (engaging surface 210) of the end wall 190 of the housing 18while at least a portion of the probe 130 is positioned as close aspossible to therotating member (i.e., in the recess defined by therecessed surface 206). Thus, the structural integrity or ability of theend wall 190 to support the probe 130 and to withstand exposure tovibration, thermal cycling, physical impact and corrosive elementswithout significant damage to the end wall 190 is enhanced.

Various features of the invention are set forth in the following claims.

We claim:
 1. A sensor for detecting the angular velocity of a rotatingmember, said sensor comprising:a bobbin having a shoulder portion and anend portion spaced from said shoulder portion, said shoulder portionfacing toward said end portion and said end portion defining an annularrecess; a coil mounted on said bobbin and within said recess; and ahousing for receiving said end portion of said bobbin to enclose saidcoil within said housing, said housing having an end wall including aninner surface and said housing also having an annular rim facing awayfrom said end wall and engaging said shoulder portion of said bobbin sothat said end portion of said bobbin is completely suspended within saidhousing and is spaced from said inner surface of said end wall.
 2. Asensor as set forth in claim 1 and further including sealing means forproviding a seal between said bobbin and said housing.
 3. A sensor asset forth in claim 1 wherein said bobbin includes an outer surfacehaving a tapered portion and said inner surface of said housing includesa tapered portion complementary with said tapered portion of said outersurface of said bobbin so as to form a one of either a taper lock and awedge fit seal between said bobbin and said housing.
 4. A sensor as setforth in claim 1 and further including at least one electricallyconductive terminal mounted on said bobbin, a lead connected to saidelectrically conductive terminal and to said coil and having a portionof said lead extending between said recess and said terminal, andsupporting means on said bobbin for supporting and positioning adjacentto said bobbin said portion of said lead extending between said recessand said terminal.
 5. A sensor as set forth in claim 4 wherein saidsupporting means includes a shelf connected to said bobbin and havingthereon a tang, said tang being spaced from said outer surface of saidbobbin so as to form between said tang and said outer surface of saidbobbin a sloped chute for receiving said portion of said lead extendingbetween said recess and said terminal, said tang and said shelfsupporting and securing said portion of said lead against said outersurface of said bobbin.
 6. A sensor as set forth in claim 1, whereinsaid coil is completely suspended within said housing and is spaced fromsaid inner surface of said end wall.
 7. A sensor as set forth in claim1, wherein said end portion of said housing comprises a closed end.
 8. Asensor as set forth in claim 3, wherein said tapered surface portionsare tapered in only one direction.
 9. A sensor as set forth in claim 3,wherein said tapered surface portions are frustoconical in shape.
 10. Asensor as set forth in claim 3, wherein said tapered surface portionsare held in place by frictional engagement only.
 11. A sensor as setforth in claim 3, wherein said tapered surface portions aresubstantially rigid.
 12. A sensor as set forth in claim 3, wherein saidouter surface portion is integral to said bobbin.
 13. A sensor as setforth in claim 3 wherein said tapered surface portions have a taperangle, and wherein said taper angle is less than about 10 degrees.
 14. Asensor as set forth in claim 3, wherein said shoulder portion of saidbobbin extends from said tapered outer surface portion.
 15. A method ofmaking a sensor for detecting the angular velocity of a rotating member,the method comprising the steps of:(a) providing a bobbin having ashoulder portion and an end portion spaced from the shoulder portion,the shoulder portion facing toward the end portion and the end portiondefining an annular recess; (b) mounting a coil on the bobbin and withinthe recess; (c) providing a housing having an end wall including aninner surface, and the housing also having an annular rim facing awayfrom the end wall; and (d) inserting the bobbin into the housing untilthe shoulder portion of the bobbin engages the annular rim of thehousing so as to prevent further movement of the bobbin into thehousing, such that the end portion of the bobbin is spaced from theinner surface of the end wall of the housing, and such that the housingencloses the coil with the housing.
 16. The method of claim 15, whereinstep (a) comprises providing the bobbin with a tapered outer surfaceportion, wherein step (c) comprises providing the housing with acomplementary tapered inner surface portion, and wherein step (d)comprises inserting the bobbin into the housing so that the taperedsurface portions engage to form a taper lock or wedge fit seal betweenthe bobbin and the housing.